<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>定义七种变量和使用变量</title>
</head>
<body>

</body>
</html>
<script>
    var num=1;
    var a1 = null;
    var a2 ;
    var a3 = 23;
    var a4 = true;
    let a5 = "这是一个字符串";
    var a6 = 10n;
    var a7 = 3.1415926;
    console.log("第二题：会在js中定义7种变量和使用变量");
    console.log("1.null:"+a1);
    console.log("2.undefined:",a2);
    console.log("3.number(整数):",a3);
    console.log("4.boolean:",a4);
    console.log("5.String:",a5);
    console.log("6.bigInt:",a6);
    console.log("7.number(小数):",a7)
</script>